Multi-speed automatic transmission

ABSTRACT

An automatic transmission includes a first planetary gear set including a first sun gear, a first pinion, and a ring gear of the first planetary gear set. The transmission includes a second planetary gear set including a second sun gear, a second pinion, and a common gear. The transmission includes a third planetary gear set including a third sun gear, the second pinion, a third pinion, and the common gear. The transmission also includes a fourth planetary gear set including the common gear, a fourth pinion, and a ring gear of the fourth planetary gear set. The second planetary gear set and the third planetary gear set form a Ravigneaux gear set. The fourth planetary gear set is concentrically arranged with the second planetary gear set or the third planetary gear set, and the second and third planetary gear sets are radially inward of the fourth planetary gear set.

BACKGROUND

I. Field of the Disclosure

This disclosure relates generally to an automatic transmission fortransmitting a rotation of an input shaft to an output shaft at a speedselected from a plurality of speeds by selectively engaging ordisengaging a plurality of torque-transmitting elements.

II. Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

In recent years, a growing demand exists for a multi-speed automatictransmission that provides a plurality of gear ratios suited to adriver's preferences. Automatic transmissions that include six or morespeeds, for example, have been proposed to augment vehicle drivability.However, as the number of speeds within these multi-speed automatictransmissions has increased, problems of packaging components within atransmission which hinder assembly of the transmission into a vehiclehave arisen.

SUMMARY

It would thus be particularly advantageous to solve packagingdifficulties in a multi-speed automatic transmission while improvingvehicle fuel efficiency and power transmission performance of thetransmission.

To overcome these shortcomings of conventional multi-speed automatictransmissions, this disclosure describes a multi-speed automatictransmission including a structure with a reduced packaging size andlow-friction components. The automatic transmission further improvesvehicle fuel efficiency by providing a wide gear ratio spread and closegear ratio steps between adjacent gear ratios, to maintain a powersupply device in an efficient operating condition. In addition, theautomatic transmission provides the close gear ratio steps to enable amore responsive torque demand logic, thus enhancing vehicle drivability.

In an aspect of the disclosure, an automatic transmission includes afirst planetary gear set including a first sun gear, a first pinion, anda ring gear of the first planetary gear set. The first sun gear mesheswith the first pinion, and the first pinion meshes with the first sungear and with the ring gear of the first planetary gear set. Thetransmission includes a second planetary gear set including a second sungear, a second pinion, and a common gear. The second sun gear mesheswith the second pinion, and the second pinion meshes with the second sungear and with the common gear. The transmission includes a thirdplanetary gear set including a third sun gear, the second pinion, athird pinion, and the common gear. The third sun gear meshes with thethird pinion, the third pinion meshes with the third sun gear and withthe second pinion, and the second pinion meshes with the third pinionand with the common gear. The transmission also includes a fourthplanetary gear set including the common gear, a fourth pinion, and aring gear of the fourth planetary gear set. The common gear meshes withthe fourth pinion, and the fourth pinion meshes with the common gear andwith the ring gear of the fourth planetary gear set. The secondplanetary gear set and the third planetary gear set form a Ravigneauxgear set. The fourth planetary gear set is concentrically arranged withthe second planetary gear set or with the third planetary gear set, andthe second and third planetary gear sets are radially inward of thefourth planetary gear set.

In the automatic transmission, the first, the second, the third, and thefourth planetary gear sets are each axially arranged on a single axis inthe automatic transmission. The first and the second planetary gear setsare separately arranged in respective first and second gear set planes.

An output shaft of the automatic transmission is directly connected tothe ring gear of the fourth planetary gear set. In the Ravigneaux gearset, the second pinion is a long pinion and the third pinion is a shortpinion. The long pinion is longer in length than the short pinion. Anumber of gear teeth of the second sun gear is greater than a number ofgear teeth of the third sun gear.

The automatic transmission further includes a first planetary carrier, asecond planetary carrier, and a third planetary carrier. The firstplanetary carrier rotatably supports the first pinion. The secondplanetary carrier rotatably supports the second pinion. The thirdplanetary carrier rotatably supports the fourth pinion.

The automatic transmission also includes a plurality oftorque-transmitting elements. A first torque-transmitting element fixesthe second sun gear when the first torque-transmitting element isengaged to transmit torque. A second torque-transmitting element fixesthe second planetary carrier when the second torque-transmitting elementis engaged to transmit torque. A third torque-transmitting element fixesthe first sun gear when the third torque-transmitting element is engagedto transmit torque. A fourth torque-transmitting element connects aninput shaft of the automatic transmission to the second sun gear whenthe fourth torque-transmitting element is engaged to transmit torque. Afifth torque-transmitting element connects the input shaft to the thirdsun gear when the fifth torque-transmitting element is engaged totransmit torque. A sixth torque-transmitting element connects the inputshaft to the third planetary carrier when the sixth torque-transmittingelement is engaged to transmit torque.

In the automatic transmission, the first, the second, and the thirdtorque-transmitting elements are packaged in a concentric arrangement,and the fourth, the fifth, and the sixth torque-transmitting elementsare packaged in a concentric arrangement. Additionally, the first, thesecond, the third, the fourth, the fifth, and the sixthtorque-transmitting elements are packaged outside of a gear train formedby the first, the second, the third, and the fourth planetary gear sets.

Three elements of the first, the second, the third, the fourth, thefifth, and the sixth torque-transmitting elements are engaged at anyspeed of the automatic transmission. The second, the third, and thefifth torque-transmitting elements are engaged in a first forward gearof the automatic transmission. The first, the third, and the fifthtorque-transmitting elements are engaged in a second forward gear of theautomatic transmission. The third, the fourth, and the fifthtorque-transmitting elements are engaged in a third forward gear of theautomatic transmission. The third, the fifth, and the sixthtorque-transmitting elements are engaged in a fourth forward gear of theautomatic transmission. The fourth, the fifth, and the sixthtorque-transmitting elements are engaged in a fifth forward gear of theautomatic transmission. The first, the fifth, and the sixthtorque-transmitting elements are engaged in a sixth forward gear of theautomatic transmission. The second, the fifth, and the sixthtorque-transmitting elements are engaged in a seventh forward gear ofthe automatic transmission. The first, the second, and the sixthtorque-transmitting elements are engaged in an eighth forward gear ofthe automatic transmission. The second, the fourth, and the sixthtorque-transmitting elements are engaged in a ninth forward gear of theautomatic transmission. In addition, the second, the third, and thefourth torque-transmitting elements are engaged in a reverse gear of theautomatic transmission.

The first forward gear includes a highest forward gear ratio of theautomatic transmission, while the ninth forward gear includes a lowestforward gear ratio of the automatic transmission. A ratio spread betweenthe highest forward gear ratio and the lowest forward gear ratio is 8.97in one embodiment. A ratio step between any two immediately adjacentforward gear ratios of the automatic transmission is less than 1.71 andgreater than 1.14 in one embodiment.

In another aspect of the disclosure, at least one of the thirdtorque-transmitting element and the fifth torque-transmitting elementmay be a locking clutch. The locking clutch includes a dog clutch.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with precise advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and the attendantadvantages thereof will be better understood by reference to theaccompanying drawings and the subsequent detailed description, where:

FIG. 1 is a schematic view of an illustrative automatic transmissionaccording to an aspect of the disclosure;

FIG. 2 is a chart describing a shift pattern for the illustrativetransmission as well as exemplary gear ratios and ratio steps;

FIG. 3 is a speed diagram showing shifting processes from a firstforward speed to a ninth forward speed, as well as a reverse speed, forthe illustrative transmission;

FIG. 4 is a graph showing the exemplary gear ratio steps betweenadjacent forward gears of the illustrative transmission;

FIG. 5 is a graph showing speed differentials at the torque-transmittingelements that are disengaged in each gear of the illustrativetransmission; and

FIG. 6 is a schematic view of an illustrative automatic transmissionaccording to a further aspect of the disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Referring to the drawings, like reference numerals designate identicalor corresponding parts throughout the several views.

In FIG. 1, reference numeral 10 denotes an illustrative automatictransmission that is used, for example, to transmit output rotation of atorque converter that is rotationally driven by a vehicle engine towheels that are driven with a speed change. The automatic transmission10 is composed of components supported about a common axis line 11 in atransmission case 12 attached to a vehicle body. These componentsinclude an input shaft 13, which may be connected to a turbine of thetorque converter that is rotationally driven by the engine. Thesecomponents also include a first planetary gear set P1, a secondplanetary gear set P2, a third planetary gear set P3, a fourth planetarygear set P4, a planetary carrier X1, a planetary carrier X2, a planetarycarrier X3, a plurality of torque-transmitting elements, and an outputshaft 14. The torque-transmitting elements include first, second, andthird clutches C1, C2, and C3, as well as first, second, and thirdbrakes B1, B2, and B3.

The planetary gear sets P1 to P4 are each axially arranged on the commonaxis line 11 in the automatic transmission. The first and the secondplanetary gear sets P1 and P2 are separately arranged in respectivefirst and second gear set planes. The third and the fourth planetarygear sets P3 and P4 are arranged in a third gear set plane that isseparate from the first and the second gear set planes. The thirdplanetary gear set P3 and the fourth planetary gear set P4 areconcentrically arranged with the third planetary gear set P3 beingradially inward of the fourth planetary gear set P4. Thus, second gearset plane is axially positioned between the first and the third gear setplanes, and the third gear set plane is a closest of the gear set planesto the input shaft 13 side of the automatic transmission.

The first planetary gear set P1 is composed of a first sun gear S1rotatably supported on the common axis line 11, the planetary carrier X1rotatably supporting a pinion set N1, and a ring gear R1 that mesheswith the first sun gear S1 through the pinion set N1.

The second planetary gear set P2 is composed of a second sun gear S2rotatably supported on the common axis line 11, the planetary carrier X2rotatably supporting a long pinion set N2, and a common gear CG thatmeshes with the second sun gear S2 through the long pinion set N2.

The third planetary gear set P3 is composed of a third sun gear S3rotatably supported on the common axis line 11, the planetary carrier X2rotatably supporting the long pinion set N2, a short pinion set N3, andthe common gear CG that meshes with the third sun gear S3 through thelong pinion set N2 and the short pinion set N3. An axial length of thelong pinion set N2 is longer than an axial length of the short pinionset N3. The second planetary gear set P2 and the third planetary gearset P3 thus form a Ravigneaux gear set.

The fourth planetary gear set P4 is composed of the common gear CGrotatably supported on the common axis line 11, a planetary carrier X3rotatably supporting a pinion set N4, and a ring gear R4 that mesheswith the common gear CG through the pinion set N4. Accordingly, aradially inward side of the common gear CG serves as the ring gear ofthe Ravigneaux gear set, and a radially outward side of the common gearCG serves as the sun gear of the fourth planetary gear set P4, such thatthe automatic transmission 10 includes an improved packaging. The fourthplanetary gear set P4 may be concentric with either the second planetarygear set P2 or the third planetary gear set P3.

FIG. 1 shows a number of gear teeth of the sun gear, the ring gear, andthe pinion gear(s) in the respective planetary gear sets P1 to P4. FIG.1 also shows a gear ratio, rho, between the sun gear and the ring gearin the respective planetary gear sets P1 to P4. Thus, in an illustrativeexample where the sun gear S1 includes 26 gear teeth, the sun gear S2includes 32 gear teeth, the sun gear S3 includes 29 gear teeth, and aradially outward side of the common gear CG (i.e. the sun gear ofplanetary gear set P4) includes 84 gear teeth, and where the ring gearR1 includes 74 gear teeth, a radially inward side of the common gear CG(i.e. the ring gear of planetary gear sets P2 and P3) includes 72 gearteeth, and the ring gear R4 includes 140 gear teeth, a value of rho forthe first planetary gear set equals 0.351, a value of rho for the secondplanetary gear set equals 0.444, a value of rho for the third planetarygear set equals 0.403, and a value of rho for the fourth planetary gearset equals 0.600.

In the first planetary gear set P1, the first sun gear S1 is fixedthrough the third brake B3. The planetary carrier X1 is directlyconnected to the ring gear R4 and to the output shaft 14. The ring gearR1 is directly connected to the planetary carrier X3. The term “directlyconnected” indicates that two elements are coupled to each other withoutany intermediate clutch or brake.

In the second planetary gear set P2, the second sun gear S2 is fixedthrough the first brake B1, and the second sun gear S2 is connected tothe input shaft 13 by engaging the first clutch C1. The planetarycarrier X2 is fixed through the second brake B2.

In the third planetary gear set P3, the third sun gear S3 is connectedto the input shaft 13 by engaging the second clutch C2.

In the fourth planetary gear set P4, the planetary carrier X3 isconnected to the input shaft 13 by engaging the third clutch C3. Thering gear R4 is directly connected to the planetary carrier X1 and theoutput shaft 14.

Three elements of the first to third brakes B1 to B3 and the first tothird clutches C1 to C3 are thus disengaged at any speed of theautomatic transmission 10. Advantageously, this reduces friction withinthe automatic transmission. The automatic transmission 10 also includesan improved assembly and a reduced packaging size. The automatictransmission 10 provides assembly and space saving benefits, inparticular, when the first to third brakes B1 to B3 and the first tothird clutches C1 to C3 lie outside of a gear train formed by theplanetary gear sets P1 to P4. Packaging the clutches and brakes outsideof the gear train also makes it easier to supply hydraulic pressure tothe clutches and brakes. Moreover, the first to third brakes B1 to B3may be packaged in a concentric arrangement, and the first to thirdclutches C1 to C3 may be packaged in a concentric arrangement. Nestingtorque-transmitting elements in one or more concentric arrangementsfurther provides the automatic transmission 10 with the advantage of areduced packaging size in an axial length of the transmission.Consequently, the automatic transmission 10 facilitates an assembly andintegration of the transmission within the vehicle body.

In the automatic transmission 10 structured as described above, arotation of the input shaft 13 is transmitted through elements of theplanetary gear sets P1 to P4 and output to the output shaft 14.Selective engagement of the first to third clutches C1 to C3 and thefirst to third brakes B1 to B3 adjusts a rotation output to the outputshaft 14, based on a speed selected from nine forward speeds and onereverse speed.

More specifically, as shown in FIGS. 2 and 3, a first forward gear ofthe automatic transmission 10 is formed when the second brake B2, thethird brake B3, and the second clutch C2 are engaged to transmit torque,while the first brake B1, the first clutch C1, and the third clutch C3are disengaged. A second forward gear is formed when the first brake B1,the third brake B3, and the second clutch C2 are engaged to transmittorque, while the second brake B2, the first clutch C1, and the thirdclutch C3 are disengaged. A third forward gear is formed when the thirdbrake B3, the first clutch C1, and the second clutch C2 are engaged totransmit torque, while the first brake B1, the second brake B2, and thethird clutch C3 are disengaged. A fourth forward gear is formed when thethird brake B3, the second clutch C2, and the third clutch C3 areengaged to transmit torque, while the first brake B1, the second brakeB2, and the first clutch C1 are disengaged. A fifth forward gear isformed when the first clutch C1, the second clutch C2, and the thirdclutch C3 are engaged to transmit torque, while the first brake B1, thesecond brake B2, and the third brake B3 are disengaged. A sixth forwardgear is formed when the first brake B1, the second clutch C2, and thethird clutch C3 are engaged to transmit torque, while the second brakeB2, the third brake B3, and the first clutch C1 are disengaged. Aseventh forward gear is formed when the second brake B2, the secondclutch C2, and the third clutch C3 are engaged to transmit torque, whilethe first brake B1, the third brake B3, and the first clutch C1 aredisengaged. An eighth forward gear is formed when the first brake B1,the second brake B2, and the third clutch C3 are engaged to transmittorque, while the third brake B3, the first clutch C1, and the secondclutch C2 are disengaged. A ninth forward gear is formed when the secondbrake B2, the first clutch C1, and the third clutch C3 are engaged totransmit torque, while the first brake B1, the third brake B3, and thesecond clutch C2 are disengaged. Additionally, a reverse gear of theautomatic transmission 10 is formed when the second brake B2, the thirdbrake B3, and the first clutch C1 are engaged to transmit torque, whilethe first brake B1, the second clutch C2, and the third clutch C3 aredisengaged.

In the automatic transmission 10, the first forward gear includes ahighest forward gear ratio of the automatic transmission, while theninth forward gear includes a lowest forward gear ratio of the automatictransmission. In an illustrative example, it is desirable that a ratiospread between the highest forward gear ratio and the lowest forwardgear ratio is 8.97. As shown in FIG. 4, it is also favorable that aratio step between any two immediately adjacent forward gear ratios ofthe automatic transmission 10 is less than 1.71. As a result, theautomatic transmission 10 maintains a power supply device in anefficient operating condition and improves vehicle fuel efficiency. Theclose gear ratio steps also enable a more responsive torque demand logicand enhance vehicle drivability. Advantageously, the torque-transmittingelements in the automatic transmission 10 have low torque requirements,so that these elements are themselves reduced in size and experiencelower friction.

In FIG. 5, exemplary speed differentials at the torque-transmittingelements that are disengaged in each gear of the automatic transmission10 are shown.

An illustrative automatic transmission 20 is depicted in FIG. 6. Theautomatic transmission 20 of FIG. 6 includes all the features of theautomatic transmission 10 of FIG. 1, with the third brake B3′implemented as a locking clutch and/or the second clutch C2′ implementedas a locking clutch. In this variation, the locking clutch may be a dogclutch instead of a higher friction multi-plate wet clutch. Each dogclutch is a low-friction element that further reduces friction withinthe automatic transmission 20 while also maintaining shift performance.In addition, implementing the third brake B3′ as a locking clutch, forexample, minimizes an efficiency concern due to a relatively high speeddifferential at B3, as shown in FIG. 5, of the automatic transmission10.

The foregoing disclosure describes merely illustrative embodiments ofthe present invention. As will be understood by those skilled in theart, the present invention may be embodied in other specific formswithout departing from the spirit or essential characteristics thereof.Accordingly, the disclosure is intended to be illustrative of thepresent invention, but not limiting of the scope of the invention, aswell as the following claims. The disclosure and any discerniblevariants of the teachings herein define, at least in part, the scope ofthe claim terminology, such that no inventive subject matter isdedicated to the public.

The invention claimed is:
 1. An automatic transmission, comprising: afirst planetary gear set including a first sun gear, a first pinion, anda ring gear of the first planetary gear set, the first sun gear mesheswith the first pinion, and the first pinion meshes with the first sungear and with the ring gear of the first planetary gear set; a secondplanetary gear set including a second sun gear, a second pinion, and acommon gear, the second sun gear meshes with the second pinion, and thesecond pinion meshes with the second sun gear and with the common gear;a third planetary gear set including a third sun gear, the secondpinion, a third pinion, and the common gear, the third sun gear mesheswith the third pinion, the third pinion meshes with the third sun gearand with the second pinion, and the second pinion meshes with the thirdpinion and with the common gear; and a fourth planetary gear setincluding the common gear, a fourth pinion, and a ring gear of thefourth planetary gear set, the common gear meshes with the fourthpinion, and the fourth pinion meshes with the common gear and with thering gear of the fourth planetary gear set; wherein the second planetarygear set and the third planetary gear set form a Ravigneaux gear set,and the fourth planetary gear set is concentrically arranged with thesecond planetary gear set or with the third planetary gear set, thesecond and third planetary gear sets being radially inward of the fourthplanetary gear set.
 2. The automatic transmission of claim 1, whereinthe first, the second, the third, and the fourth planetary gear sets areeach axially arranged on a single axis in the automatic transmission. 3.The automatic transmission of claim 1, wherein an output shaft of theautomatic transmission is directly connected to the ring gear of thefourth planetary gear set.
 4. The automatic transmission of claim 1,wherein in the Ravigneaux gear set, the second pinion is a long pinionand the third pinion is a short pinion, the long pinion being longer inlength than the short pinion, and a number of gear teeth of the secondsun gear is greater than a number of gear teeth of the third sun gear.5. The automatic transmission of claim 1, further comprising: a firstplanetary carrier that rotatably supports the first pinion; a secondplanetary carrier that rotatably supports the second pinion; and a thirdplanetary carrier that rotatably supports the fourth pinion.
 6. Theautomatic transmission of claim 5, further comprising: a firsttorque-transmitting element that fixes the second sun gear when thefirst torque-transmitting element is engaged to transmit torque; asecond torque-transmitting element that fixes the second planetarycarrier when the second torque-transmitting element is engaged totransmit torque; a third torque-transmitting element that fixes thefirst sun gear when the third torque-transmitting element is engaged totransmit torque; a fourth torque-transmitting element that connects aninput shaft of the automatic transmission to the second sun gear whenthe fourth torque-transmitting element is engaged to transmit torque; afifth torque-transmitting element that connects the input shaft to thethird sun gear when the fifth torque-transmitting element is engaged totransmit torque; and a sixth torque-transmitting element that connectsthe input shaft to the third planetary carrier when the sixthtorque-transmitting element is engaged to transmit torque.
 7. Theautomatic transmission of claim 6, wherein the first, the second, andthe third torque-transmitting elements are packaged in a concentricarrangement, and the fourth, the fifth, and the sixthtorque-transmitting elements are packaged in a concentric arrangement.8. The automatic transmission of claim 6, wherein the first, the second,the third, the fourth, the fifth, and the sixth torque-transmittingelements are packaged outside of a gear train formed by the first, thesecond, the third, and the fourth planetary gear sets.
 9. The automatictransmission of claim 6, wherein three elements of the first, thesecond, the third, the fourth, the fifth, and the sixthtorque-transmitting elements are engaged at any speed of the automatictransmission.
 10. The automatic transmission of claim 6, wherein: thesecond, the third, and the fifth torque-transmitting elements areengaged in a first forward gear of the automatic transmission, thefirst, the third, and the fifth torque-transmitting elements are engagedin a second forward gear of the automatic transmission, the third, thefourth, and the fifth torque-transmitting elements are engaged in athird forward gear of the automatic transmission, the third, the fifth,and the sixth torque-transmitting elements are engaged in a fourthforward gear of the automatic transmission, the fourth, the fifth, andthe sixth torque-transmitting elements are engaged in a fifth forwardgear of the automatic transmission, the first, the fifth, and the sixthtorque-transmitting elements are engaged in a sixth forward gear of theautomatic transmission, the second, the fifth, and the sixthtorque-transmitting elements are engaged in a seventh forward gear ofthe automatic transmission, the first, the second, and the sixthtorque-transmitting elements are engaged in an eighth forward gear ofthe automatic transmission, the second, the fourth, and the sixthtorque-transmitting elements are engaged in a ninth forward gear of theautomatic transmission, and the second, the third, and the fourthtorque-transmitting elements are engaged in a reverse gear of theautomatic transmission.
 11. The automatic transmission of claim 10,wherein: the first forward gear includes a highest forward gear ratio ofthe automatic transmission, and the ninth forward gear includes a lowestforward gear ratio of the automatic transmission.
 12. The automatictransmission of claim 11, wherein a ratio spread between the highestforward gear ratio and the lowest forward gear ratio is 8.97, and aratio step between any two immediately adjacent forward gear ratios ofthe automatic transmission is less than 1.71 and greater than 1.14. 13.The automatic transmission of claim 6, wherein at least one of the thirdtorque-transmitting element and the fifth torque-transmitting element isa locking clutch.
 14. The automatic transmission of claim 13, whereinthe locking clutch is a dog clutch.